The present invention relates to microwave phase shifter devices, and more particularly to 180.degree. phase shift devices having the further capability of a solid-state aperture shutter that can be selected to produce either a reflection of uniform amplitude and phase in one mode of operation, or to absorb RF energy that enters the radiating aperture in the other mode.
Devices are known in the art which provide the function of a selectable 180.degree. phase shift transition. For example, U.S. Pat. No. 4,070,639 describes a 180.degree. microwave phase-bit device implemented in a stripline medium with integral coupling into a waveguide by means of an H plane loop within the waveguide. PIN-diode switches are employed to reverse the direction of current in the loop.
Another microwave phase shifter device is described in "Integrated Diode Phase-Shifter Elements for an X-Band Phased-Array Antenna," Mark E. Davis, IEEE Transactions on Microwave Theory and Techniques, December, 1975, pages 1080-1084. A 180.degree. phase bit device is described which employs PIN diodes to selectively reverse the direction of current flow in a ring hybrid to achieve reversal of the RF phase.
Radar systems engineers are paying increased attention to aperture designs that allow substantial reductions in the radar cross section (RCS) of airborne platforms. Another concern is potential damage to delicate electronics in or immediately behind the radiating elements due to directed or stray high-level RF radiation as, for example, on the flight deck of an aircraft carrier.
A major disadvantage of the prior art devices is that it does not incorporate the significant features of protection from high-level RF energy and low reflected signal levels at a uniform phase angle.